Nanoparticles of Co 0.5 Ni 0.5−2x Li x Fe 2+x O 4 with x ranging from 0.00 to 0.25 in steps of 0.05 were prepared by using citrate precursor method. The microstructure and the magnetic properties of the as-prepared nanosamples and the effect of increasing Li 1+ ions on their physical properties were studied. X-ray diffraction (XRD), transmission electron microscopy (TEM), particle size analyzer (PSA), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM) were used to investigate the samples. The XRD analysis confirmed the cubic spinel phase formation of the prepared samples, while TEM images and PSA ensure the nanostructural features of them. The FTIR spectra reveal the presence of two prominent absorption bands v 1 and v 2 in the range of 600 and 400cm −1 which are usually attributed to the tetrahedral and octahedral complexes of the spinel lattice, respectively. The change of v 2 gradually towards lower frequency and the slightly change of v 1 were explained depending on the effect of increasing Li 1+ content on the bond length of B-site metal ions and the spin canting of A-site metal ions, respectively. Saturation magnetization and remnant magnetization were found to increase with adding Li 1+ ions up to x=0.15 and then to decrease again, while coercivity decreases monotonically by increasing Li 1+ ions. The change in magnetic properties by adding Li 1+ ions is explained as to be dependent on many factors such as crystallite size, measured density, porosity, expected cation distribution, A–B exchange interactions, and magnetocrystalline anisotropy.